A CB requires only a couple amps. One of the buck switching regulators on Amazon would do a fine job for just a few bucks.
Here's an example:
https://www.amazon.com/EPBOWPT-Conve...72&sr=8-3&th=1

OR, you could have a full blown dual system, with either two 12V alternators in series (as in my M-715), of a modified center tapped 24V alternator. If you are interested in this, I will post the paper I wrote on the subject.